JPH08103786A - Aerobic treatment of organic wastewater - Google Patents

Abstract

(57) [Summary] [Purpose] Excess sludge generation can be suppressed at low cost by solubilizing sludge under mild conditions and without reducing load and treatment efficiency. We propose an aerobic treatment method for organic wastewater that can reduce the generation of excess sludge to zero. [Structure] The organic waste liquid 13 is introduced into an upstream portion 32 of the aeration tank 11 partitioned by a partition plate 31, and mixed with activated sludge and return sludge 14 in the aeration tank 11 to perform aerobic treatment, and the upstream portion. The mixed solution of 32 is drawn out, the drawn solution 22 is introduced into the ozone treatment tank 21 to treat the sludge with ozone, and the ozone treated solution 25 is returned to the downstream portion 33 of the aeration tank 11 for aerobic treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aerobic treatment method of organic waste liquid for controlling the production of excess sludge, and particularly to an organic waste treatment for solubilizing sludge under mild conditions to suppress the production of excess sludge. The present invention relates to a liquid treatment method.

[0002]

2. Description of the Related Art An aerobic treatment method for treating organic wastewater under aerobic conditions by utilizing the action of aerobic microorganisms, such as an activated sludge treatment method, produces a large amount of hardly dehydratable excess sludge. It is difficult to generate and process. Conventionally, such excess sludge has been disposed of, but it is difficult to secure a disposal site for it, and it is necessary to reduce the volume of sludge.

As one of the aerobic treatment methods, there is a complete oxidation method. This method is a method of performing aerobic treatment in the same manner as a normal method by reducing the sludge load, and since the amount of self-digestion of sludge increases relative to the amount of sludge growth, excess sludge can be extremely reduced. However, this method requires a low tank load and is not practical when the amount of drainage is large.

On the other hand, a usual aerobic treatment is carried out,
A method is used to reduce the volume of excess sludge produced. Anaerobic digestion methods and aerobic digestion methods are generally used as such sludge volume reduction methods. In these methods, a sludge anaerobic digestion apparatus or an aerobic digestion apparatus is provided separately from an aerobic treatment apparatus for organic wastewater, and sludge is digested under anaerobic or aerobic conditions.

However, in these methods, only about 50% of the treated sludge is decomposed, and the rest is discharged as digested sludge. Since this digested sludge is a biologically inactive substance, it cannot be reduced in volume any more and must be incinerated or discarded.

As another method for reducing the volume of excess sludge, the excess sludge is subjected to physicochemical treatment such as ozone treatment,
A method of conducting aerobic digestion by introducing it to an aerobic digester (Japanese Patent Publication No. 57-19719), or by adding an alkali to excess sludge and heating to hydrolyze and solubilize it.
A method for treating excess sludge by neutralizing the decomposed liquid and returning it to the aerobic treatment device has been proposed (Japanese Patent Publication No. Sho 49-1181).
No. 3). However, such a conventional method has a low volume reduction rate, and the treatment conditions have become strict because methods of ozone treatment and heat treatment have not been sufficiently examined, which makes process control difficult, and High cost was invited.

Further, in Japanese Patent Laid-Open No. 6-206088, an amount of activated sludge larger than the amount of sludge grown by assimilation of BOD in the liquid to be treated is withdrawn from the aerobic treatment system, and the extracted sludge is subjected to ozone treatment. A method for aerobic treatment of organic effluent introduced into a gas treatment system is described. FIG. 3 shows the processing flow, 1 is an aerobic treatment system, 2 is an ozone treatment system,
Reference numeral 11 is an aeration tank, 12 is a sludge separation unit, and 21 is an ozone treatment tank. The tank liquid in the aeration tank 11 is ozone-treated and then returned to the aeration tank 11.

To treat the organic waste liquid according to the flow of FIG. 3, first, the liquid to be treated 13 is introduced into the aeration tank 11, mixed with the return sludge 14 and the activated sludge in the aeration tank 11, and the air supply passage 16 is provided. Air supplied from the air diffuser 15 is diffused to perform aerobic treatment. The aerobic treatment liquid is introduced into the sludge separation unit 12 from the communication path 17 and solid-liquid separated. The separated liquid is discharged as the treatment liquid 18, and a part of the separated sludge 19 is returned to the aeration tank 11 as the returned sludge 14. When the excess sludge 20 is generated, it is discharged to the outside of the system.

In the ozone treatment system 2, the liquid in the tank of the aeration tank 11 is drawn out, this drawn sludge 22 is introduced into the ozone treatment tank 21, and ozone 24 is supplied from the lower part of the ozone treatment tank 21 to remove the drawn sludge 22. The sludge is converted to BOD by contacting it with ozone 24 and performing ozone treatment. The ozone-treated sludge 25 is returned to the aeration tank 11 for aerobic treatment.

In the above method, the amount of excess sludge generated can be reduced to zero by subjecting the drawn-out sludge 22, which is larger than the multiplied sludge, to ozone treatment. However, in such a conventional method, the liquid in the aeration tank 11 is in a completely mixed state. However, sludge in such a completely mixed state is difficult to be subjected to ozone treatment or other solubilization treatment, and the sludge is subjected to BOD. To achieve this, it is necessary to raise the injection rate of ozone or the like or the heating temperature.

[0011]

DISCLOSURE OF THE INVENTION An object of the present invention is to solubilize sludge under mild conditions at low cost, without lowering load and treatment efficiency.
The object of the present invention is to propose a method for aerobic treatment of organic waste liquid which can suppress the generation of excess sludge and can even reduce the generation of excess sludge in some cases.

[0012]

The present invention, in an aerobic treatment system having an aeration section and a solid-liquid separation section, aerobically treats organic waste liquid in the presence of activated sludge containing aerobic microorganisms. Process and step of returning part of the separated sludge solid-liquid separated in the solid-liquid separation section to the aeration section as return sludge, and withdrawing a part of the mixed liquid containing activated sludge and return sludge from the aeration section A method of aerobically treating an organic drainage solution, which comprises a step of introducing a solubilization treatment solution into an aeration section after using a plug flow type aeration tank as the aeration section,
This is an aerobic treatment method for an organic waste liquid, characterized in that a part of the mixed liquid is drawn out from the upstream portion of the plug flow type aeration tank, solubilized and introduced into the aeration portion.

The organic effluent to be treated in the present invention is an effluent containing an organic substance which is treated by a usual aerobic biological treatment method, but it contains a hardly decomposable organic substance or an inorganic substance. Good. Examples of such organic effluents include sewage, night soil, food factory effluents and other industrial effluents.

In the method for aerobic treatment of organic waste liquid, a certain amount of activated sludge containing aerobic microorganisms is held in the aerobic treatment system,
An organic waste liquid is introduced into this and brought into contact with it under aerobic conditions, and BOD in the liquid to be treated is decomposed by the oxidizing action of aerobic microorganisms. At this time, an aerobic treatment is performed using a plug flow type aeration tank as the aeration section of the aerobic treatment system. As a result, the BOD in the liquid to be treated is assimilated and the activated sludge grows.

In the conventional general method, in order to retain a certain amount of activated sludge in the aerobic treatment system, the same amount of activated sludge as that propagated by assimilation of BOD is discharged as excess sludge, The volume of the excess sludge discharged has been reduced. Therefore, even if the excess sludge is decomposed by hydrolysis or the like and returned to the aerobic treatment system, the excess sludge is generated. Even in the method of Japanese Patent Laid-Open No. 6-206088, in which a large amount of activated sludge is extracted and solubilized, the extracted sludge is a completely mixed sludge, and the solubilization conditions are severe.

On the other hand, in the present invention, a part of floating activated sludge in the liquid to be treated, preferably floating activated sludge larger than the amount of sludge grown by assimilation of BOD in the liquid to be treated, is subjected to plug flow (one direction). Flow) type aeration tank
This is solubilized by the method described below and then introduced into an aerobic treatment system for aerobic biological treatment to convert the drawn-out sludge into BOD under mild conditions and suppress the apparent growth of activated sludge. As a result, the amount of excess sludge is reduced, and depending on the conditions, the amount of excess sludge generated can be reduced to zero.

The aerobic treatment system in the present invention is a treatment system for treating an organic effluent in the presence of activated sludge containing aerobic microorganisms. As such a treatment system, an organic waste liquid is mixed with activated sludge in an aeration tank and aerated, the mixed liquid is subjected to solid-liquid separation by a solid-liquid separation device, and a part of the separated sludge is returned to the aeration tank. A treatment system based on the standard activated sludge treatment method is generally used, but other treatment systems obtained by modifying this may be used.

In the present invention, a part of the mixed liquid containing activated sludge is extracted from the upstream portion of the plug flow type aeration tank and solubilized, and the solubilized liquid is aerobically treated. The solubilization means may be any means capable of converting sludge into biodegradable one, such as oxidation treatment with ozone or the like, heat treatment, hydrolysis with alkali or the like, and ozone treatment is preferable. By extracting the mixed solution from the upstream portion of the plug flow type aeration tank as described above and performing the solubilization treatment, compared to the case of performing the solubilization treatment on the mixed liquid or excess sludge extracted from the complete mixing type aeration tank, Even if the solubilization treatment is performed under mild conditions, the same sludge volume reduction rate can be obtained. If the solubilization treatment is performed under the same conditions, the sludge volume reduction rate can be further increased. The reason for this is not clear, but the upstream part of the aeration tank has a higher load than the downstream part, aerobic microorganisms are in the logarithmic growth phase, and the surface structure of the microorganisms in this logarithmic growth phase is changed by the solubilization treatment. It is presumed that this is because it is easy.

The solubilization conditions are ozone in the case of ozone treatment.
Injection rate 0.002-0.1g-O ₃/ G-SS, preferred
Specifically 0.005-0.06g-O₃/ G-SS
You.

To make the aeration tank a plug flow type, 2
Two or more independent tanks are installed in series; one aeration tank is divided into two or more in the direction perpendicular to the direction in which the organic drainage flows; one aeration tank in the direction in which the organic drainage flows It is divided into two or more parts in the parallel direction to be elongated; a method such as using an elongated aeration tank can be adopted. By these methods, it becomes difficult for the liquid to mix in the upstream portion and the downstream portion in the aeration tank. A plate-shaped partition plate or the like can be used to partition one aeration tank.

FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction in the present invention. In the figure, 1 is an aerobic treatment system and 2 is a solubilization treatment system. Aerobic processing system 1
Like an activated sludge treatment device, it is a treatment system that aerobically decomposes organic waste liquid by contacting it with activated sludge, and an aeration tank (aerobic treatment tank) and a solid-liquid separation unit may be provided separately. However, it is shown as an overall processing system including these. The solubilization treatment system 2 is a device that solubilizes sludge in the drawing liquid drawn from the upstream portion of the aeration tank and converts it into BOD.

The aerobic treatment system 1 of FIG. 1 holds a certain amount of activated sludge 3a for aerobic treatment. When the liquid to be treated 4 is introduced into the aerobic treatment system 1 and subjected to aerobic treatment, the BOD contained in the liquid to be treated 4 is assimilated into the activated sludge 3a, and a new sludge 3b is generated due to the multiplication thereof. To do. On the other hand, the activated sludge 3a in the system is self-decomposed, and the self-decomposed portion 3c disappears. So in steady state,
The difference between the generated sludge 3b and the self-decomposed content 3c grows as the grown sludge 3d.

In the conventional volume reduction method, the breeding sludge 3d generated here is discharged outside the system as excess sludge, and the volume of this excess sludge is reduced, so about 50% of the excess sludge is further converted to digested sludge. Had been discharged. Alternatively, in Japanese Patent Publication No. 49-11813, the breeding sludge 3d discharged as excess sludge is hydrolyzed to be solubilized and returned to the aerobic treatment system 1. In this treatment method, it is added as a hydrolysis liquid. BOD newly generates generated sludge, and excess sludge is generated by continuing the treatment.

A case where the sewage treatment system 2 is used to treat the breeding sludge 3d which has been conventionally discharged as surplus sludge is shown by a broken line 5 in FIG. BOD generated by solubilization when returned to 1
Is converted into sludge and another generated sludge 3e is generated, and this amount becomes a substantial sludge growth amount and must be discharged as excess sludge. Thus, the sludge volume reduction rate when solubilizing the grown sludge 3d and returning it to the aerobic treatment system is 30 to 40% by weight of the grown sludge 3d, which is lower than in the case of anaerobic or aerobic digestion.

On the other hand, a larger amount of the extracted sludge 3f than the propagated sludge 3d is extracted from the upstream portion of the plug flow type aeration tank of the aerobic treatment system 1, solubilized by the solubilization treatment system 2 and converted into BOD. Convert and solubilize treatment liquid 6 to aerobic treatment system 1
By returning to the aeration tank of No. 3, the solubilization can be performed under mild conditions, and another 3 g of produced sludge is produced from the BOD produced by the solubilization treatment. In this case, the difference between the drawn sludge 3f and the produced sludge 3g becomes the mineralized portion 3h.

Here, a larger amount of the extracted sludge 3f than the propagated sludge 3d is solubilized and converted into BOD.
Compared with the case where only the propagated sludge 3d is subjected to ozonolysis or hydrolysis, the mineralized portion is increased and the sludge volume reduction rate is increased. When the amount of drawn sludge 3f is determined so that the multiplied sludge 3d and the mineralized portion 3h are equal, the excess sludge becomes substantially zero. When the amount of the grown sludge 3d is larger than that of the mineralized portion 3h, the difference becomes the substantially increased portion 3i, and the excess sludge 7
Is discharged outside the system. Reference numeral 8 is a treatment liquid of the aerobic treatment system 1.

In the aerobic treatment system 1, the aeration tank capacity is V, the activated sludge concentration is X, the sludge yield is Y, the treated liquid flow rate (treatment liquid flow rate) is Q, the organic matter concentration of the treated liquid is Ci,
The concentration of organic matter in the treated liquid is Ce, the concentration of biologically treated organic matter is (Ci-Ce), the sludge self-decomposition constant is Kd, the excess sludge discharge amount is q, the amount drawn into the solubilization treatment tank is Q ', and the solubilization treatment is performed. The mass balance is expressed by the following equation [1], where k is the ratio of the converted sludge reconverted to activated sludge.

[Equation 1] V dX / dt = Y Q (Ci-Ce) -V Kd X-q X-Q′X + k Q′X [1]

In the equation [1], V dX / dt is the change amount of the activated sludge 3a in the aerobic treatment system 1, and Y Q (C
i-Ce) is the amount of produced sludge 3b, V Kd X is the amount of self-decomposition 3c, qX is the amount of excess sludge 7 discharged, Q'X is the amount of extracted sludge 3f, and k Q'X is the amount of produced sludge 3g. The amount is shown.

Here, Q (Ci-Ce) / V = LV (tank load), q / V = 1 / SRT (excess sludge retention time ratio),
Q '/ V = θ (circulation ratio of activated sludge to the solubilization treatment system),
If (1-k) = δ (mineralization rate) is set, in the steady state,
The formula [1] is simplified as the following formula [2].

## EQU00002 ## Y LV / X = Kd + 1 / SRT + .delta..theta. [2]

In the usual aerobic treatment system in which the solubilization treatment system 2 does not exist, the third term (δθ) in the equation [2] does not exist, so that when the sludge load is constant, the excess sludge amount (X / SR
T) is determined. On the other hand, in the treatment system in which the solubilization treatment system is combined, as is apparent from the equation [2], the excess sludge is reduced in volume by the value of the third term. Under the condition that the value of the third term is comparable to the value of the second term, the sludge load can be set to a normal value without discharging the excess sludge (1 / SRT = 0). is there.

[0031]

Embodiments of the present invention will be described below. FIG. 2 is a flow sheet showing an aerobic treatment method for an organic waste liquid according to an embodiment, in which the aeration tank is partitioned in the direction perpendicular to the direction of the flow of the organic waste liquid to be a plug flow type, and the solubilization treatment is performed. As an example, an ozone treatment is shown. In the figure,
The same reference numerals as those in FIG. 3 indicate the same or corresponding parts. The aerobic treatment system 1 includes an aeration tank 11, a solid-liquid separation device 12, a pump P ₁ ,
And the flow paths associated therewith.
The ozone treatment system 2 is composed of an ozone treatment tank 21 for solubilization, a pump P ₂ and a flow path associated with these. The aeration tank 11 is partitioned into an upstream portion 32 and a downstream portion 33 by a partition plate 31, and is configured as a plug flow type.

In the treatment method of FIG. 2, in the aerobic treatment system 1, the liquid to be treated 13 is introduced into the starting end of the upstream portion 32 of the aeration tank 11 and mixed with the return sludge 14 and the activated sludge in the aeration tank 11. , The air supplied from the air supply paths 16a and 16b is diffused from the air diffusers 15a and 15b, and the upstream portion 3
2 and the downstream part 33 are subjected to aerobic treatment. in this case,
Since the inside of the aeration tank 11 is partitioned by the partition plate 31,
Even if air is diffused from the air diffusers 15a and 15b, it is difficult to mix the in-tank liquid (mixed liquid) in the upstream portion 32 and the mixed liquid in the downstream portion. Therefore, the BOD load of the upstream portion 32 becomes higher than that of the downstream portion 33, and the activated sludge is maintained in a logarithmic growth state. The BOD load of the upstream portion 32 is usually 0.5 kg
-BOD / kg-MLSS · day or more, preferably 1
It is desirable to be set to 3 kg-BOD / kg-MLSS · day. By carrying out the aerobic treatment in this manner, organic substances are decomposed by a biooxidation reaction. The mixed liquid in the upstream portion 32 moves from the flow path 34 to the downstream portion 33 as the mixed liquid in the downstream portion 33 is introduced into the solid-liquid separation device 12 from the end portion.

A part of the aerobic treatment liquid in the downstream portion 33 is introduced into the solid-liquid separation device 12 from the communication path 17 and solid-liquid separation is performed. The separated liquid is discharged as the treatment liquid 18, and a part of the separated sludge 19 is returned to the upstream portion 32 of the aeration tank 11 by the pump P ₁ as the returned sludge 14.

In the ozone treatment system 2, a part of the mixed liquid is drawn out by the pump P ₂ from an arbitrary position in the upstream portion 32 of the aeration tank 11, and the drawn liquid 22 is introduced into the upper part of the ozone treatment tank 21 to carry out the ozone treatment. Ozone 24 is supplied from the lower part of the tank 21, the extraction liquid 22 is brought into contact with the ozone 24, and ozone treatment is performed to convert the activated sludge in the extraction liquid into BOD. The ozone treatment liquid 25 is returned to an arbitrary position in the downstream portion 33 of the aeration tank 11, preferably to the starting end side of the downstream portion 33, and aerobically treated as a load. The ozone exhaust gas is discharged from the exhaust ozone passage 23.

The amount of ozone supplied to the ozone treatment tank 21 (ozone injection rate) is 0.002 to 0.1 g-O ₃ / g.
-SS, preferably 0.005~0.06g-O ₃ / g
-SS is desirable. Upstream portion 32 as described above
Figure 3
The ozone injection rate to obtain the same sludge volume reduction rate is smaller than that in the case where ozone is treated by extracting the mixed solution from a completely mixed aeration tank like the one described above. Can be processed with.

In the case of FIG. 2, V in the formula [1] is the capacity of the aeration tank 11, X is the concentration of the total sludge held in the aeration tank 11 and the solid-liquid separation device 12 with respect to V, and Q'is the aeration tank 11. It is calculated as the capacity when the sludge concentration of the concentrated sludge in the inside or the solid-liquid separation device 12 is converted into X. Thereby, as shown in FIG. 1, each value can be determined as the aerobic treatment system 1.

In FIG. 2, it is possible to reduce the volume of the sludge by treating the extracted liquid with ozone so that the amount of the extracted sludge is larger than that of the multiplied sludge. However, when the excess sludge 20 is not zero, the excess sludge 20 Is discharged out of the system. When the amount of drawn liquid is determined so that the sludge and mineralized part are the same,
The amount of excess sludge generated will be zero. Even in this case, some sludge can be discharged in a system in which an inorganic substance such as sand is accumulated.

COD which is usually hardly decomposed by ozone treatment
A small amount of components are produced, but such persistent COD
The components can be decomposed by, for example, introducing a carrier such as a sponge into the upstream portion and / or the downstream portion of the aeration tank 11 and supporting sludge on the carrier to increase the SRT. Further, when the amount of the withdrawal liquid 22 to be ozone-treated increases, the biological treatment performance may deteriorate. In such a case, however, a carrier for supporting sludge is provided in the upstream portion and / or the downstream portion of the aeration tank 11. By maintaining a certain amount of sludge, the biological treatment performance can be maintained high.

Although the ozone treatment liquid 25 is returned to the downstream portion 33 of the aeration tank 11 in FIG. 2, it can be returned to the upstream portion 32 or may be introduced into another aerobic treatment system to perform aerobic treatment. You can also Further, although the aeration tank 11 is divided into two parts in FIG. 2, it may be divided into three or more parts. In this case, it is preferable to draw out the mixed solution in the most upstream part, subject it to ozone treatment, and return it to the downstream side. Further, a plurality of independent aeration tanks may be used instead of the aeration tank 11 as shown in FIG. 2, and whether the inside of the tank is elongated in the direction from the inlet of the liquid to be treated 13 to the communication path 17. Alternatively, it is also possible to use an aeration tank or the like which is divided so as to be elongated.

Next, a test example will be described. Test Example 1 According to the method shown in FIG. 2, the organic waste liquid was aerobically treated. For organic drainage, 1: 1 by weight of peptone
Synthetic wastewater consisting of yeast extract (BOD 200 mg /
1) was used. The processing conditions and results are shown in Table 1.

Comparative Example 1 The same organic waste liquid as in Test Example 1 was treated according to the method shown in FIG. The processing conditions and results are shown in Table 1.

[0042]

[Table 1] * 1 Percentage of total sludge volume

From the results in Table 1, in the case of Test Example 1, the sludge conversion rate per BOD was 0.05 g-SS / g-BOD even when the ozone injection rate was lowered to 0.02 g-O ₃ / g-SS. It can be seen that the sludge volume reduction rate is large compared to 0.17 g-SS of Comparative Example 1 and is large.

[0044]

According to the method for aerobic treatment of organic waste liquid of the present invention, since the mixed solution is extracted from the upstream portion of the plug flow type aeration tank and subjected to the solubilization treatment, the solubilization treatment is performed under mild conditions. It is also possible to reduce the volume of surplus sludge and reduce the generation of surplus sludge to zero in some cases at a low cost and without lowering the load and treatment efficiency.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the principle of sludge volume reduction in the present invention.

FIG. 2 is a flow sheet showing an aerobic treatment method for organic waste liquid according to an embodiment.

FIG. 3 is a flow sheet showing a conventional method for aerobic treatment of organic waste liquid.

[Explanation of symbols]

 1 Aerobic treatment system 2 Ozone treatment system 3a Activated sludge 3b, 3e, 3g Produced sludge 3c Self-decomposition 3d Proliferation sludge 3f Extracted sludge 3h Mineralized portion 3i Increased portion 4 Treated liquid 6 Solubilized treatment liquid 7 Excess sludge 8 treatment Liquid 11 Aeration tank 12 Solid-liquid separator 13 Liquid to be treated 14 Returned sludge 15, 15a, 15b Air diffuser 16, 16a, 16b Air supply passage 17 Connection passage 18 Treatment liquid 19 Separation sludge 20 Excess sludge 21 Ozone treatment tank 22 Extraction Liquid 23 Waste ozone passage 24 Ozone 25 Ozonated liquid 31 Partition plate 32 Upstream part 33 Downstream part 34 Flow path

Claims (1)

[Claims] 1. A step of aerobically treating an organic waste liquid in the presence of activated sludge containing aerobic microorganisms in an aerobic treatment system comprising an aeration section and a solid-liquid separation section, and a solid-liquid separation section. The step of returning a part of the solid-liquid separated sludge to the aeration section as return sludge, and withdrawing a part of the mixed solution containing activated sludge and return sludge from the aeration section, solubilizing the extracted solution, and then removing An aerobic treatment method for an organic waste liquid, which comprises a step of introducing a solubilization treatment liquid into an aeration section, wherein a plug flow type aeration tank is used as the aeration section, and a mixed liquid is supplied from an upstream portion of the plug flow type aeration tank. An aerobic treatment method for an organic waste liquid, which comprises extracting a part of the water, solubilizing it, and introducing it into the aeration section.